Polyarylalkane-terminated, solvent-resistant polycarbonate resins as photoconductors

ABSTRACT

Polyarylalkane-terminated polycarbonate resins are disclosed which when utilized in photoconductive layers and elements show superior stability and resistance to lixiviation by the carrier liquid of liquid xerographic developers.

O Umted States Patent [151 3,660,083 Bloom et al. 4 1 May 2, 1972 [s41POLYARYLALKANE-TERMINATED, [56] References Cited SOLVENT-RESISTANT NlTEDSTATES PA NT POLYCARBONATE RESINS AS U TE S PHOTOCONDUCTORS 3,542,547 11/1970 Wilson ..96/1.6 2,999,750 9/1961 Miller et al.. ..252/501 X [72]lnventors: Melvin S. Bloom; Stewart H. Merrill, both 3,408,186 10/1968Mamminom. ..96/ 1.5 of Rochester, N.Y. 3,542,544 1 1/1970 Seus et al..96/1 .5 [73] Assigneez Eastman Kodak Company, Rochester 3,567,6863/1971 White et a] ..260/47 XA Primary Examiner-Charles E. Van Horn [22]Filed: June 25, 1970 Att0rneyW. H. J. Kline, Paul R. Holmes and J. Wm.Berkstresser 21 App]. No.: 49,953

[57] ABSTRACT [52] US. CL... ..96/ 1.5, 96/1 PC, 260/47 XA,polyarylalkane4erminated polycarbonate resins are disclosed 1 17/37 LEwhich when utilized in photoconductive layers and elements [51] 'f CL eC038 5/ 02 show superior stability and resistance to lixiviation by thecar- [58] Field of Search ..96/1.5, 1.6; 252/501; tier liquid fli idXerographic deve]opers 2 Claims, No Drawings POLYARYLALKANE-TERMINATED,SOLVENT- RESISTANT POLYCARBONATE RESINS AS PHOTOCONDUCTORS Thisinvention relates to electrophotography, and in particular tophotoconductive compositions and elements.

The process of xerography, as disclosed by Carlson in U.S. Pat. No.2,297,691, employs an electrophotographic element comprising a supportmaterial bearing a coating of a normally insulating material whoseelectrical resistance varies with the amount of incident electromagneticradiation it receives during an imagewise exposure. The element,commonly termed a photoconductive element, is first given a uniformsurface charge, generally in the dark after a suitable period of darkadaptation. It is then exposed to a pattern of actinic radiation whichhas the effect of differentially reducing the potential of this surfacecharge in accordance with the relative energy contained in various partsof the radiation pattern. The differential surface charge orelectrostatic latent image remaining on the electrophotographic elementis then made visible by contacting the surface with a suitableelectroscopic marking material. Such marking material or toner, whethercontained in an insulating liquid or on a dry carrier, can be depositedon the exposed surface in accordance with either the charge pattern ordischarge pattern as desired. Deposited marking material can then beeither permanently fixed to the surface of the sensitive element byknown means such as heat, pressure, solvent vapor, or the like, ortransferred to a second element to which it can similarly be fixed.Likewise, the electrostatic charge pattern can be transferred to asecond element and developed there.

Various photoconductive insulating materials have been employed in themanufacture of electrophotographic elements. For example, vapors ofselenium and vapors of selenium alloys deposited on a suitable supportand particles of photoconductive zinc oxide held in a resinous,film-forming binder have found wide application in the present-daydocument copying applications.

Since the introduction of electrophotography, a great many organiccompounds have also been screened for their photoconductive properties.As a result, a very large number of organic compounds have been known topossess some degree of photoconductivity. Many organic compounds haverevealed a useful level of photoconduction andhave been incorporatedinto photoconductive compositions.

Typical of these organic photoconductors are the triphenylamines and thetriarylmethane leuco bases, Optically clear photoconductor-containingelements having desirable electrophotographic properties can beespecially useful in electrophotography. Such electrophotographicelements can be expose through a transparent base if desired, therebyproviding unusual flexibility in equipment design. Such compositions,when coated as a film or layer on a suitable support, also yield anelement which is reusable; that is, it can be used to form subsequentimages after residual toner from prior images has been removed bytransfer and/or cleaning. in particular liquid developers have foundwide acceptance for such elements because of the high resolution imagesthey make possible. Unfortunately the carrier liquid of conventionalliquid developers attacks most known photoconductor systems and by aprocess called lixiviation leaches or otherwise removes photoconductorcompounds, binders, sensitizers and the like from the element. Furtherthe element can be softened and then mechanically injured during use.

Thus far, the selection of various compounds suitable for incorporationinto photoconductive compositions to form electrophotographic layers hasproceeded on a compound-bycompound basis. Effective prediction of thetypes of compounds which will exhibit desired properties from among thelarge number of different photoconductive substances available isdifficult.

It is, therefore, an object of this invention to provide novelbinder-photoconductors containing elements which exhibit highphotosensitivity when electrically charged and are resistant to attackby conventional carrier liquids.

It is another object to provide photoconductor-containing compositionswhich in addition exhibit high electrical speeds.

It is a further object of the invention to provide an improved processutilizing the photoconductive elements described herein.

Also, it is yet another object of this invention to provide solventresistant electrophotographic elements.

These and other objects of the invention are accomplished by providingcertain polycarbonate resins with photoconductive substituents generallyselected from moieties of substituted triarylmethane compounds. Such abinder-photoconductor compound resists lixiviation when utilized inelectrophotographic elements used with liquid development. Lixiviationof the photoconductor out of the photoconductive element and into theliquid developer has produced erratic results such as non-uniformdevelopment, contamination of the developer, and limited the useful lifeof the photoconductor element to extremely short run cycles which couldbe as low as l or 2 cycles depending on the rate of extraction of thephotoconductor from the light-sensitive element.

The preferred polymer-photoconductor compositions or oligomers of thepresent invention are generally isopropylidenediphenol polycarbonatepolymers. terminated with photoconductor moieties characterized by thefollowing general formula:

0H, CH i (c211. 2N "N(C2H5)2 wherein R is selected from the groupconsisting of a hydroxyl group, a carboxy group, an hydroxy-alkoxy groupor an amino group and R is hydrogen, alkyl or alkoxy or the like.

Electrophotographic elements prepared with the oligomers of the presentinvention can be prepared in a conventional manner such as, for example,by blending a dispersion of solution of the oligomer and additionalphotoconductor or binder when necessary or desirable together with otheraddenda and coating or forming a self-supporting layer with'the oligomercontaining material. Addenda useful in the practice of the presentinvention are generally supplemental materials added, i.e., dyes and thelike which are useful for changing the spectral sensitivity orelectrophotosensitivity of the element prepared therefrom whereparticular effects are desired.

The photoconductive layers of the invention can also be sensitized bythe addition of effective amounts of sensitizing compounds to exhibitimproved electrophotosensitivity. Sensitizing compounds useful with theoligomers of the present invention can be selected from a wide varietyof materials, including such materials as pyrylium dye salts includingthiapyrylium dye salts and selenapyrylium dye salts disclosed inVanAllen et al. U.S. Pat. No. 3,250,615; fluorenes, such as7,l2-dioxo-l3-dibenzo(a,h)fluorene, 5,l0-dioxo-4a,lldiazabenzo(b)fluorene, 3,13-dioxo-7-oxadibenzo(b,g)fluorene, and thelike; aggregate-type sensitizers of the type described in Belgian Pat.No. 705,1 17 dated Apr. 16, 1968; aromatic nitro compounds of the kinddescribed in U.S. Pat. No. 2,610,120; anthrones like those disclosed inU.S. Pat. No. 2,670,284; quinones, U.S. Pat. No. 2,670,286;benzophenones U.S. Pat. No. 2,670,287; thiazoles U.S. Pat. No.2,732,301; mineral acids; carboxylic acids, such as maleic acid, diandtri-chloroacetic acids, and salicyclic acid; sulfonic and phosphoricacids; and various dyes, such as cyanine (including carbocyanine),merocyanine, diarylmethane, thiazine, azine, oxazine, xanthene,phthalein, acridine, azo, anthraquinone dyes and the like and mixturesthereof. The sensitizers preferred for use with the oligomers of thisinvention are selected from pyrylium salts including selenapyryliumsalts and thiapyrylium salts, and cyanine dyes including carbocyaninedyes.

Where a sensitizing compound is employed with the oligomer to form asensitized electrophotographic element, it is the normal practice to mixa suitable amount of the sensitizing compound with the coatingcomposition so that, after thorough mixing, the sensitizing compound isuniformly distributed in the coated element. Other methods ofincorporating the sensitizer or the effect of the sensitizer may,however, be employed consistent with the practice of this invention. Inpreparing the photoconductive layers, no sensitizing compound isrequired to give photoconductivity in the layers which contain thephotoconducting substances, therefore, no sensitizer is required in aparticular photoconductive layer. However, since relatively minoramounts of sensitizing compound give substantial improvement in speed insuch layers, the sensitizer is preferred. The amount of sensitizer thatcan be added to a photoconductor-incorporating layer to give effectiveincreases in speed can vary widely. The optimum concentration in anygiven case will vary with the specific oligomer and sensitizing compoundused. In general, substantial speed gains can be obtained where anappropriate sensitizer is added in a concentration range from about0.0001 to about 30 percent by weight based on the weight of thefilmforming coating composition. Normally, a sensitizer is added to thecoating composition in an amount by weight from about 0.005 to about 5.0percent by weight of the total coating composition.

Preferred polycarbonate resins utilized or useful in the preparation ofthe oligomers of the present invention include4,4-isopropylidenediphenol polycarbonate.

Solvents useful for preparing coating compositions with the oligomers ofthe present invention can include a wide variety of organic solvents forthe components of the coating composition. For example, benzene;toluene; acetone; 2-butanone; chlorinated hydrocarbons such as methylenechloride; ethylene chloride; and the like; ethers, such astetrahydrofuran and the like, or mixtures of such solvents canadvantageously be employed in the practice of this invention.

In preparing the coating compositions utilizing the oligomers disclosedherein useful results are obtained where the photoconductive substanceis present in an amount equal to at least about 1 weight percent of thecoating composition. The upper limit in the amount of photoconductivematerial present can be widely varied in accordance with usual practice.It is normally required that the photoconductive material be present inan amount ranging from about 1 weight percent of the coating compositionto about 99 weight percent of the coating composition. A preferredweight range for the photoconductive material in the coating compositionis from about l weight percent to about 60 weight percent.

Coating thicknesses of the photoconductive composition on a support canvary widely. Normally, a wet coating thickness in the range of about0.001 inch to about 0.01 inch is useful in the practice of theinvention. A preferred range of coating thickness is from about 0.002inch to about 0.006 inch before drying although such thicknesses canvary widely depending on the particular application desired for theelectrophotographic element.

Suitable supporting materials for the photoconductive layers of thepresent invention can include any of the electrically conductingsupports, for example, various conducting papersi aluminum-paperlaminates; metal foils, such as aluminum foil, zinc foil, etc.; metalplates, such as aluminum, copper, zinc, brass, and galvinized plates,vapor deposited metal layer such as silver, nickel or aluminum onconventional film supports such as cellulose acetate, poly(ethyleneterephthalate), polystyrene and the like conducting supports.

An especially useful conducting support can be prepared by coating atransparent film support material such as poly(ethylene terephthalate)with a layer containing a semiconductor dispersed in a resin. A suitableconducting coating can be prepared from the sodium salt of acarboxyester lactone of a maleic anhydride-vinyl acetate copolymer,cuprous iodide and the like. Such conducting layers and method for theiroptimum preparation and use are disclosed in U.S. Pat. Nos. 3,007,901,3,245,833 and 3,267,807.

. The oligomer compositions of the present invention can be employed inphotoconductive elements useful in any of the well knownelectrophotographic processes which require photoconductive layers. Onesuch process is the xerographic process. In a process of this type, anelectrophotographic element held in the dark, is given a blanketpositive or negative electrostatic charge as desired, by placing itunder a corona discharge to give a uniform charge to the surface of thephotoconductive layer. This charge is retained by the layer owing to thesubstantial dark insulating property of the layer, i.e., the lowconductivity of the layer in the dark. The electrostatic charge formedon the surface of the photoconductive layer is then selectivelydissipated from the surface of the layer by imagewise exposure to lightby means of a conventional exposure operation such as for example, by acontact-printing technique,,or by lens projection of an image, or reflexor bireflex techniques and the like, to thereby form a latentelectrostatic image in the photoconductive layer. Exposing the surfacein this manner forms a pattern of electrostatic charge by virtue of thefact that light energy striking the photoconductor causes theelectrostatic charge in the light struck areas to be conducted away fromthe surface in proportion to the illuminance on a particular area.

The charge pattern produced by exposure is then developed or transferredto another surface and developed there, i.e., either the charged oruncharged areas are rendered visible, by treatment with a mediumcomprising electrostatically responsive particles having opticaldensity. The developing electrostatically responsive particles can be inthe form of a dust, or powder and generally comprise a pigment in aresinous carrier called a toner. A preferred method of applying such atoner to a latent electrostatic image for solid area development is bythe use of a magnetic brush. Methods of forming and using a magneticbrush toner applicator are described in the following US. Pat. Nos.:2,786,439; 2,786,440; 2,786,441; 2,811,465; 2,874,063; 2,984,163;3,040,704; 3,117,884 and reissue Re 25,779. Liquid development of thelatent electrostatic image may also be used. In liquid development thedeveloping particles are carried to the image-bearing surface in anelectrically insulating liquid carrier. Methods of development of thistype are widely known and have been described in the patent literature,for example, U.S. Pat. No. 2,297,691 and in Australian Pat. No. 212,315.In dry developing processes the most widely used method of obtaining apermanent record is achieved by selecting a developing particle whichhas as one of its components a low-melting resin. Heating the powderimage then causes the resin to melt or fuse into or on the'element. Thepowder is, therefore, caused to adhere permanently to the surface of thephotoconductive layer. In other cases, a transfer of the charge image orpowder image formed on the photoconductive layer can be made to a secondsupport such as paper which would then become the final print afterdeveloping and fusing or fusing respectively. Techniques of the typeindicated are well known in the art and have been described in a numberof U.S. and foreign patents, such as U.S. Pat. Nos. 2,297,691 and2,551,582, and in RCA Review, Vol. 15 (1954) pages 469-484.

The oligomer compositions of the present invention can be used inelectrophotographic elements having many structural variations. Forexample, the photoconductive composition can be coated in the form ofsingle layers or multiple layers on a suitable opaque or transparentconducting support. Likewise, the layers can be contiguous or spacedhaving layers of insulating material or other photoconductive materialbetween layers or overcoated or interposed between the photoconductivelayer or sensitizing layer and the conducting layer. It is also possibleto adjust the position of the support and the conducting layer byplacing a photoconductor layer over a support and coating the exposedface of the support or the exposed or overcoated face of thephotoconductor with a conducting layer. Configurations differing fromthose contained in the examples can be useful or even preferred for thesame or different application for the electrophotographic element. 5

The following examples are included for a further understanding of thisinvention.

EXAMPLE 1 In this example photoconductors were made whereinpolycarbonate oligomers were terminated with a photoconductor moleculehaving a single hydroxyl group. Specifically, a short (average length,four units) isopropylidenediphenol polycarbonate was terminated withbis(4-diethylamino-2-methyl-phenyl)-[3-methoxy-4-(2-hydroxyethoxy)phenyl]me thane in thefollowing manner: to a solution of 5.0 g. (0.010 mole) of bis(4-diethylamino-Z-methyl-pheny1)-[3-methoxy- 4-( 2-hydroxyethoxy)phenyllmethane and 4.6 g. (0.020 mole) of 4,4-isopropylidenediphenol inml of dry methylene chloride and I0 ml of dry pyridine was addeddropwise 2.6 g. (0.026 mole) of phosgene in ml of dry methylene chloridewith stirring at This mixture was then extracted successively withexcess dilute hydrochloric acid, three portions of water, 5 percentaqueous sodium bicarbonate and water again. The product was precipitatedby pouring the organic solution into isopropyl alcohol. When tested inthe photoconductor system disclosed in Light et al, British Pat. No.l,l53,506 i.e. Lexan polycarbonate plus photoconductor plus4-(4-dimethylaminophenyl)-2,6-diphenyl thiapyrylium perchlorate 2%) thefollowing data were obtained:

Conc.,

percent Electrical H and D" Leach-out of total speeds 1 shoulder/toetest, percent compo- OP extracted Photoconductor sition in 4 hrs.

Control (see Example 1) 20 6, 100/768 5, 230/000 2 2. 0 Control 5. 0Oligomer of Ex. 2 20 2, 500/100 2, 000/330 0, l Oligomer of Ex. 2 5012,000/1, 000 8, 000/800 0. 1

1 The sensitizer utilized in this case was 4-(4-dimcthylamino-phenyn-2,6-diphenyl thiapyrylium fiuoroborate.

2 3 hours.

3 The oligomer contains 77 percent cfiective photoconductive.

It will be thus noted that the oligomer photoconductors appear to offerboth low leachability and good electrophotographic speeds. Furthermore,it should be noted that merely adding high molecular weight groups tothe photoconductor does not necessarily decrease its leachability. Thusin the following table it will be noted that merely increasing the sizeof R in the general structure does not necessarily decrease theleachability of the photoconductor.

H .C.H...N@ e

Leach-out test H and D electrical (percent photocon- 1 The oligomcrcontains only 50 percent effective photoconductor.

Q Extraction rate was determined from a static soaking of one squareinch of sample film in 10 ml. of Isopar G followed by ultravioletabsorption spectroscopical analysis of the supernatant liquid.

3 Bis(4-diethylanlinc-Z-methylphenyl)phenylmethane. 4 3 hours.

EXAMPLE 2 To increase the photoconductor content in the oligomer, asingle bisphenol unit was coupled through carbonate groups with asimilar monohydroxy compound, bis (4-diethylamino-2-methyl-phenyl)-4-(2-hydroxyethoxy)phenylmethane in the followingmanner:

To a solution of 10 g. (.02l mole) of bis(4-diethyl-amino-2-methyl-phenyl)-[4-(2-hydroxyethoxy)phenyl]methane in 10 ml of drymethylene chloride and 5 ml of dry pyridine was added over severalminutes a solution of 3.8 g. (0.0ll mole) of 4,4-isopropylidenediphenylbischloroformate in 10 ml of dry methylene chloride. After the mixturewas stirred an hour it was extracted with aqueous sodium bicarbonate andthe organic layer was poured into ethanol to precipitate the crudeproduct. This material, in 40 ml of methylene chloride, was extractedwith aqueous sodium bicarbonate then shaken with l percent aqueoussodium dithionite to discharge the green color. After extraction withtwo portions of water the organic solution was poured into isopropylalcohol to precipitate an amorphous solid which softens at about 105.

Anal. Calculated for C H N O found:

PERCENT PHOTOCONDUCTOR EXTRACTED BY ISOPAR G 0.8M OP percent extractedaiter R 1 hr. 4 hrs.

-CHzOHzCH3 0.1 0.1

In addition to the foregoing oligomer precursors other bisphenols andglycols other than 4,4'-isopropylidenediphenyl may be used. Additionallyother triphenylmethane derivatives have demonstrated utility in thepreparation of the oligomers.

The invention has been described in detail with particular reference topreferred embodiments thereof but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:

1. An electrophotographic element resistant to lixiviation by liquiddevelopers, said element comprising a conductive support having thereona photoconductive composition comprising an oligomeric isopropylidenediphenol polycarbonate terminated withbis(4-diethylamino-2-methyl)-(4-substituted phenyl)methanephotoconductor moieties.

2. In an electrophotographic process wherein a photoconductive elementis charged, imagewise exposed, and liquid developed, the improvementwherein said element is comprised of a conductive support having thereona photoconductive composition comprising an oligomeric isopropylidenediphenol polycarbonate terminated with bis(4-diethylamino-2-methyl)-(4-substituted phenyl)methane photoconductor moieties.

2. In an electrophotographic process wherein a photoconductive elementis charged, imagewise exposed, and liquid developed, the improvementwherein said element is comprised of a conductive support having thereona photoconductive composition comprising an oligomeric isopropylidenediphenol polycarbonate terminated withbis(4-diethylamino-2-methyl)-(4-substituted phenyl)methanephotoconductor moieties.